Thin films are used in many devices. The stability of these devices is often determined by the degradation of the thin films and/or their interaction with adjacent materials.
Ferroelectric and high dielectric constant materials have been suggested as materials to obtain new and improved results in various applications. One application is in forming capacitors based on these materials. These eventual materials can be integrated on a chip with a silicon-based device. However, issues exist as part of integrating the material that is used. Preparation of the Ferroelectric and high dielectric materials are performed at relatively high temperatures, e.g. 400 to 800xc2x0 C., in oxidizing environments. This imposes limitations on the choice of a suitable electrode material.
In addition, the use of complex compositions may cause undesired reactions, and possible deterioration of the materials. One approach to minimize undesirable interactions between such materials is to insert a barrier layer between the materials. This layer should be stable in its contact with its adjacent materials. The barrier should also hinder the diffusion of adjacent species across it. In applications where an electrical current must be able to flow across the layer, as is the case of contacts to electronic devices, the barrier layer also needs to be electrically conducting. Barriers have been used to block certain diffusion types. However, the use of a barrier results in a complex multi-layered electrode/barrier structure.
One suggested operation has been to deposit a contact on a polysilicon substrate, and to deposit a ferroelectric electrode on the contact. The deposition is done between 400 and 700xc2x0 C., e.g. 500xc2x0 C., using MOCVD. The deposited ferroelectric material is annealed under a partial pressure of oxygen in order to nucleate and grow a crystalline ferroelectric phase. This oxidizing environment grows the crystal at a high partial pressure of oxygen.
In the prior art, this oxygen has caused certain problems. The oxygen moves along the material, and can oxidize surfaces on the material. For example, the contact layer on the polysilicon is often itself a silicon material. A thin layer of a non-oxidizing contact material, such as platinum is often placed on the silicon. The platinum can itself oxidize, or material below the platinum can oxidize. The polysilicon underlayer can also oxidize. A diffusion barrier can be formed to prevent the oxygen from entering the polysilicon.
Alternatives to the platinum electrode have been suggested. A ruthenium dioxide electrode has been suggested, for example in xe2x80x9cElectrode Structures for Integration of Ferroelectric or High Dielectric Constant Films in Semiconductor Devicexe2x80x9d Albert Grill, IBM Research Division, 1999. Ruthenium dioxide forms an efficient material, However, ruthenium dioxide is not xe2x80x9cfully oxidizedxe2x80x9d, On heating, ruthenium dioxide can react to form a volatile RuO4 compound which evaporates to gas. The disassociation leaves ruthenium dioxide crystals.
Nicolet et al. has suggested using ternary thin films of the type TMxe2x80x94Sixe2x80x94N. This introduces an additional compound (N) into the mix of compounds. This additional compound raises a possibility of additional undesired reactions.
The present application teaches a conducting layer, formed on an electrically active structure, the conductive layer being formed of a ternary oxide material having first and second immiscible compounds, said first and second immiscible compounds having one common oxygen element, which are formed in an amorphous state, and are meta-stable relative to one another over a specified range. An embodiment describes a specific material for use in forming contacts which have specific advantageous properties; including high resistance to oxidation, electrical conductivity, and formation of a block to the passage of certain materials such as oxygen.
A specific material described herein is an electrically-conducting fully oxidized transition metal compound combined with an oxide of a different material, where the two materials are immiscible at the temperature range of interest and in combination form an amorphous material. The transition metal can be any of a number of desired transition metals, with preferred materials being ruthenium, (Ru) iridium (Ir) and osmium (OS). other materials are described herein.
The additional oxide can be an oxide of Silicon or of another material. Silicon is preferred since the SiO2 material is generally grown on a silicon substrate which can prevent additional reactions.
On particularly interesting material is a ternary material of the type Ruxe2x80x94Sixe2x80x94O.
Another material is a ternary thin film of the type Tmxe2x80x94Sixe2x80x94O where Tm is a transition metal of the Ti, V, chromium groups.